Using data from the Herschel Space Observatory, astronomers have detected for the first time cold water vapor enveloping a dusty disk around a young star. The findings suggest that this disk, which is poised to develop into a solar system, contains great quantities of water, suggesting that water-covered planets like Earth may be common in the universe. Herschel is a European Space Agency mission with important NASA contributions.

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Scientists have previously found warm water vapor in planet-forming disks close to a central star. Evidence for vast quantities of water extending out into the cooler, far reaches of disks where comets take shape had not been seen until now. The more water available in disks for icy comets to form, the greater the chances that large amounts eventually will reach new planets through impacts.

"Our observations of this cold vapor indicate enough water exists in the disk to fill thousands of Earth oceans," said astronomer Michiel Hogerheijde of Leiden Observatory in The Netherlands. Hogerheijde is the lead author of a paper describing these findings in the Oct. 21 issue of the journal Science.

In our solar system, surface oceans of water appear to be unique to Earth, but some of our neighboring planets and moons appear to be awash in a variety of bodies ranging from oceans of ice to methane seas to subsurface liquid oceans spanning an entire moon or planet.

TW Hydrae, located 175 light-years away from Earth, is between 5 million and 10 million years old. Compared with the 4.5-billion-year-old sun of ours, it is very young. The star is so young and so close to Earth that scientists look to it for a picture of what our own solar system looked like in its early years. Most captivating of all is TW Hydrae’s spinning disk of gas, dust, water and other planet-building materials; it stretches 200 astronomical units (AU) from the star (one AU is the sun-to-Earth distance). By comparison, the dwarf planet Pluto at its farthest orbital distance is only 49 AU from the sun.

The frigid, watery haze detected by Hogerheijde and his team is thought to originate from ice-coated grains of dust near the disk's surface. Ultraviolet light from the star causes some water molecules to break free of this ice, creating a thin layer of gas.

As the new solar system evolves, icy comets are likely to deposit much of the water they contain on freshly created worlds through impacts, giving rise to oceans. Astronomers believe TW Hydrae and its icy disk may be representative of many other young star systems, providing new insights on how planets with abundant water could form throughout the universe.